I think what Eagle is talking about is the Andy Mark Plaction Wheels (Plastic + Traction = Plaction)
www.andymark.com/SearchResults.asp?Cat=103
Last year we (Team 876) went with the Roughtop and possibly using them again this year. We were able to go over the bumps last year with little to no problem and we were able to push other robots with pretty good success.
Here's what it looked like(
http://www.chiefdelphi.com/media/photos/35059)
I think if there was sand or dirt that the robot had to drive over the Wedgetop would be the way to go, but since there is carpet, Roughtop would probably be a better choice.